Thin film magnetic recording medium with controlled grain morphology and topology

ABSTRACT

A magnetic storage medium is composed of a non-wettable substrate upon which a transient liquid metal layer is deposited and maintained as a distribution of discontinuous liquid features. A magnetic film layer is deposited on the transient liquid metal layer resulting in a reaction of the liquid metal with the magnetic film. The topology of the magnetic film is controllable by adjusting the thickness of the transient liquid metal layer.

This application is a continuation of application Ser. No. 07/417,371filed Oct. 5, 1989, now abandoned.

BACKGROUND OF THE INVENTION

The present invention relates to a method of manufacturing a magneticthin film medium with controlled grain morphology and topology. Moreparticularly the invention is directed to a magnetic medium in which amagnetic thin film is deposited on a thin transient liquid metal layerdeposited onto a non-wettable substrate, the surface topology andmagnetic characteristics of the medium being controlled by adjustment ofthe thickness of the transient liquid metal underlayer and thedeposition conditions.

The demand for increased capacity of storage media has resulted in thedevelopment of the magnetic thin film disk. The magnetic thin film diskshould have a high and controllable coercivity, preferably in the rangebetween 600 and 2000 Oe, and a high remanent magnetization. Binary orternary cobalt-based alloys, such as CoCr, CoRe, CoPt, CoNi, CoNiCr,CoPtCr and the like are commonly used as the magnetic material inthin-film magnetic disk technology. Platinum is one of the key elementsin achieving high coercivity, of greater than 900 Oe, required fordisks. Depending upon the required range of coercivity, up to 20 percentof Pt can be added to Co based alloy.

The magnetic film is deposited on a non-magnetic substrate, typicallyNiP-coated Al-Mg or glass disks. The recording density of a medium isinversely proportional to the distance (fly height) between the disk anda magnetic head with which the information is being recorded. Thus thesurface of the disk substrate should be extremely smooth to permit alower fly height. However the extreme smoothness of&the disk generallyresults in a high contact area between the disk and head which, in turn,results in a high value of stiction or friction The high stiction orfriction can cause damage to the disk, recording head and its assemblyas well as disk drive motors. In order to alleviate the problem, anovercoat, typically carbon, as well as a lubricant are applied to theoutermost film layer. However, extremely smooth disks even wi-h alubricant coating may still exhibit unacceptably high stiction andfriction levels. Moreover, over a period of time the lubricant isremoved from the disk surface. Therefore, a controlled surface topologyor texture is required to enhance flyability and lubricant retention.

In order to overcome the problems of high stiction and friction, priorto the deposition of the magnetic layer the surface of the disksubstrate is roughened by one of the common mechanical abrasivetechniques known as texturing.

The mechanical texturing usually is associated with the formation ofweldments and asperities along the texture lines. These weldments canresult in an increase in fly height as well as severe wear of themagnetic layer during operation of the disk. Therefore, it is desirableto texture or roughen the substrate surface by means other thanmechanical abrasion while not adversely affecting the disk magneticproperties.

It is also desirable to enhance coercivity of the magnetic disks whilereducing the quantity and expense of platinum element additions.

In U.S. Pat. No. 4,539,264 entitled "Magnetic Recording Medium" amagnetic recording medium is described as having a non-magneticsubstrate, a bismuth layer of less than 100Å thick and a magnetic metalthin film formed on the bismuth layer. While the described mediumachieves increased coercivity levels, the bismuth layer remains as adiscrete underlayer and the topological and alloying effects resultingfrom a transient liquid metal layer are not achieved. The patent alsofails to suggest the application of a layer of metal film between thebismuth layer and the magnetic layer which is an alternative embodimentof the present invention.

SUMMARY OF THE INVENTION

The present invention overcomes the above difficulties by applying anunderlayer of a transient liquid metal film between a non-wettablesubstrate and the magnetic thin film. The transient liquid metal layeris applied while the substrate, which is not wettable by the liquidmetal, is maintained at a condition at which the liquid metal is in aliquid state, and preferably at a temperature above the melting point ofthe transient liquid metal. The result is that the liquid metal iscaused to "ball-up" and form a layer of disconnected molten metalfeatures. Instead of forming a distinct underlayer, a distribution ofthe concentration of the transient liquid metal across the grain of themagnetic layer is manifest. The transient liquid metal elements may be,but are not limited to, gallium, indium, tin, bismuth, lead, cadmium,mercury, selenium, tellurium and their alloys with other metalsincluding silver, palladium, platinum, or gold as well as binary orternary compounds of the transient liquids themselves. The preferredtransient liquid metals are gallium, indium and tin. The substrate canbe, but is not limited to, silicon dioxide, glass, polymers, or metalsubstrates treated in such a manner to be rendered non-wetting to thetransient liquid metal, with glass being the preferred substratematerial. The magnetic thin film may be an alloy of which cobalt is amajor constituent, preferably Co-Pt-Cr, Co-Cr, Co-Ni-Cr, Co-Re.

In order to manufacture the medium in accordance with the presentinvention, the substrate is held at a temperature above or close to themelting point of the transient liquid metal during deposition of thetransient liquid metal layer onto the substrate by conventionalsputtering, evaporation, plating or other deposition techniques as areknown in the art. The outer magnetic film layer is then deposited ontothe transient liquid metal at either an elevated temperature above themelting point of the transient liquid metal or alternatively at a moreconventional lower temperature at which the underlayer features, whileundercooled, are nevertheless metastably liquid. The transient liquidmetal will become alloyed with the magnetic layer thereby imparting tothe magnetic layer a controlled topology which provides a disk surfacewith improved tribology. The magnetic medium will not include a puretransient liquid metal underlayer.

The advantages of the present invention include the elimination of thevariability and dependence upon direction of the magnetic properties,control of the magnetic film surface roughness and control of thecoercivity of the medium.

It will be apparent to those skilled in the art that the area of themedium surface subject to roughening can be limited by the use of knownmasking techniques.

When the described interaction between the magnetic film layer and thetransient liquid metal underlayer is undesirable, it is possible toapply a metal film layer between the underlayer and a magnetic filmouterlayer which will not adversely affect the surface topology.Moreover, the application of such an additional layer permits control ofthe surface topology over a wider range of roughness to improve thetribology while maintaining the coercivity of the film constant.Preferred metal films for the interlayer are, but not limited to,chromium, molybdenum, vanadium, palladium and platinum, or alloys ofthese metals.

A principal object of the present invention is therefore, the provisionof a magnetic medium with controlled surface morphology and topology,and magnetic characteristics.

Another object of the invention is the provision of a method ofmanufacturing a magnetic medium composed of a non-wetting substrate, atransient liquid metal underlayer, and a magnetic film outer layer.

A further object of the invention is the provision of a magnetic mediumcomposed of a non-wetting substrate, a transient liquid metal underlayerand a magnetic film layer where the surface roughness of the magneticfi-m layer is controllable by adjustinq the transient liquid metalunderlayer thickness and deposition temperature.

A still further object of the invention is the provision of a magneticmedium composed of a non-wetting substrate, a transient liquid metalunderlayer, a metallic film interlayer and a magnetic film outerlayer.

An object of the invention is the provision of a method of manufacturinga magnetic medium composed of a non-wetting substrate, a transientliquid metal layer, a metallic film interlayer and a magnetic filmouterlayer.

Further and still other objects of the present invention will becomemore clearly apparent when the following description is read inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1A is a cross-sectional representation of a transient liquid metallayer deposited on substrate in accordance with the present invention;

FIG. 1B is a cross-sectional representation of a magnetic mediummanufactured in accordance with the present invention;

FIGS. 2A to 2D are SEM images of the surface topology evaporated galliumfilm of 25, 50, 100 and 200Å average thickness respectively applied to asilicon dioxide substrate;

FIGS. 3A to 3D are SEM images of the surface topology of the structuresobtained by when sputter depositing 750Å of Co-Pt-Cr alloy film over 25,50, 100 and 200Å thick film of Ga respectively on a silicon dioxidesubstrate;

FIG. 4 is a SEM image of the surface topology of a sputtered Co-Pt-Crfilm without any transient liquid metal underlayer;

FIG. 5 is a graphical representation of the magnetic properties of 750Åthick Co-Pt-Cr film without any underlayer;

FIG. 6 is a graphical representation of the magnetic properties of 750Åthick Co-Pt-Cr film sputtered on a 25Å thick layer of gallium depositedonto a clean silicon dioxide substrate;

FIG. 7 is a graphical representation of the magnetic properties of 750Åthick Co-Pt-Cr film sputtered onto a 50Å thick layer of galliumdeposited on a clean silicon dioxide sub-strate;

FIG. 8 is a graphical representation of the magnetic properties of 750Åthick Co-Pt-Cr film sputtered onto a 100Å thick layer of galliumdeposited on a clean silicon dioxide sub-strate;

FIG. 9 is a graphical representation of the magnetic properties of 750Åthick Co-Pt-Cr film sputtered onto a 200Å thick layer of galliumdeposited on a clean silicon dioxide substrate;

FIG. 10 is a cross-sectional representation of an alternative preferredmagnetic medium manufactured in accordance with the present invention;

FIG. 11 is a SEM image of surface topology of a 750Å thick layer ofCo-Pt-Cr alloy film applied onto an interlayer of 100Å thick Cr filmwhich is applied on a 100Å thick layer of gallium deposited on a silicondioxide substrate; and

FIG. 12 is a graphical representation of the coercivity of Co-Pt-Cralloy film deposited onto a Cr interlayer film deposited on a galliumunderlayer of different thicknesses.

DETAILED DESCRIPTION

Referring now the FIGURES and to FIG. 1A in particular, there is shownin accordance with the present invention a substrate 10 such as silicondioxide, glass, polymer or thin coating thereof on any suitablenon-magnetic storage disk material. The substrate is selected to benon-wettable by liquid metals.

As used in the context of this invention, the term non-wettable refersto the break up of a liquid uniformly deposited film to form adistribution of disconnected liquid metal features due to the lack ofwetting or interaction between a substrate and the liquid metal.

Deposited upon the substrate is an underlayer of a transient liquidmetal 12 such as gallium, indium, tin, bismuth, lead, cadmium, mercury,selenium, tellurium and their alloys with other elements, includingsilver, palladium, platinum or gold as well as binary or ternarycompounds of the transient liquid metals themselves. The preferredtransient liquid metals are gallium, indium and tin. The average film 12thickness is the range between approximately 25Å and 300Å, preferably inthe range between 25Å and 100Å. The term transient liquid metal layerrefers to the temporary existence of the liquid metal layer, until adeposition of a sufficient quantity of a magnetic alloy material resultsin the dissolution and reaction of the liquid metal in the magneticalloy, with the substantially complete disappearance of the liquid phasefrom the magnetic medium structure. As a result, in the final magneticmedium there is no distinct transient liquid metal film layer, butrather there is an intergranular segregation of such metal, as shown inFIG. 1B. The transient liquid metal layer is applied to the substratewhile the substrate is maintained at a temperature in excess of themelting point of the transient liquid metal. In the example of a galliumfilm, the substrate is held at a temperature above approximately 30° C.during transient liquid metal deposition. Due to the poor wetting of thesubstrate by the liquid metal, the liquid metal forms spherical featuresas shown in FIG. 1A.

The transient liquid metal film underlayer is applied onto the substrateby conventional means such as vapor deposition or sputtering and thelike while the substrate is maintained at a temperature above themelting point of the transient liquid metal. A magnetic film 14 isdeposited onto the transient liquid metal film layer in a conventionalmanner with the substrate and transient liquid metal being held eitherat a temperature above the melting point of the transient liquid metalor at any lower conventionally used temperature at which the transientliquid metal underlayer still exists in a liquid state. If theunderlayer is allowed to solidify prior to deposition of the magneticlayer, it will exist in the resulting magnetic medium as a discretelayer and may adversely affect the mechanical and adhesion properties ofthe magnetic disk. The magnetic film preferably is Co-Pt-Cr but anyother magnetic thin film material may also be used in practicing theinvention. The thickness of the magnetic film is in the range between100Å and 1500Å, preferably in the range between 200Å and 1000Å.

The surface of magnetic film 14 generally follows the topology of thespherical structures of the transient liquid metal layer and exhibitsregions of increased concentration of the transient liquid metal 18,e.g. gallium, in the area between the resulting magnetic film grains andin the area where the spherical structures were originally located.

As is well known in the art, a top coat, typically carbon, and alubricant can be applied to the magnetic medium and is required for manyapplications. Such a treatment is fully compatible with the magneticmedium described herein.

While in the prior art the substrate has been mechanically roughened tocontrol the topology of the subsequently deposited magnetic film layer,problems have occurred as mentioned above. In accordance with theteachings of the present invention, the magnetic film layer topology iscontrolled by adjusting the thickness of the transient liquid metallayer thereby obviating the problems associated with mechanicalroughening while maintaining, and even improving, the magneticproperties of the medium.

FIG. 2A to 2D are scanning electron microscope images of evaporatedgallium films deposited over a silicon dioxide substrate at atemperature above the melting point of gallium. By virtue of thenon-wettability of the substrate, rather than the gallium forming asmooth uniform film layer, the gallium forms many spherical structuresor features. The quantity of the spherical structures and the sizedistribution of the structures are dependent upon the average thicknessof the gallium layer, temperature of the substrate during deposition,and the degree of wetting of the substrate by the transient liquidmetal. The degree of wetting of the substrate can be affected by theaddition of alloying elements to the gallium, particularly alloyingelements that strongly interact with the substrate material.

The thickness dependency in the case of pure gallium deposited onto asilicon dioxide substrate maintained at 32° C. to 35° C. duringdeposition is shown in FIGS. 2A to 2D. FIG. 2A is a scanning electronmicroscope image of a 25Å thick layer of evaporated gallium film on asilicon dioxide substrate. FIG. 2B is a scanning electron microscopeimage of a 50Å thick layer of evaporated gallium film on a silicondioxide substrate. FIG. 2C is a scanning electron microscope image of a100Å thick layer of evaporated gallium film on a silicon dioxidesubstrate. FIG. 2D is a scanning electron microscope image of a 200Åthick layer of evaporated gallium film on a silicon dioxide substrate.

It will be apparent from the FIGS. 2A to 2D that the quantity of thespherical structures per unit surface area decreases with increasinggallium film layer thickness and the size of the spherical structuresincreases with increasing gallium film layer thickness.

In manufacturing a preferred embodiment of the medium a 750Å thickCo-Pt-Cr alloy magnetic film layer is deposited over a layer of galliumwhich was previously deposited on a silicon dioxide substrate. Thegallium will dissolve or alloy with the cobalt, platinum and chromiumand the gallium layer will in effect disappear as a distinct film layer.The surface topology of the magnetic film layer is shown in the scanningelectron microscope images of FIGS. 3A to 3D. In FIG. 3A a 750Å thickmagnetic film layer was deposited over a 25Å average thickness layer ofgallium. In FIG. 3B a 750Å thick magnetic film layer was deposited overa 50Å average thickness layer of gallium. In FIG. 3C a 750Å thickmagnetic film layer was deposited over a 100Å thick magnetic film layer.In FIG. 3D a 750Å thick magnetic film layer was deposited over a 200Åaverage thickness layer of gallium.

Examination of the FIGS. 3A to 3D shows that with increasing underlayerfilm thickness, there is manifest in the magnetic film layer surfacefewer and larger spherical structures. It will be apparent to thoseskilled in the art that the surface topology and morphology of the outermagnetic film layer is controllable by the selection of the averagethickness of the transient liquid metal film underlayer.

As a comparison and to further demonstrate the effect of the transientliquid metal underlayer, FIG. 4 is a scanning electron microscope imageof the surface of a layer of Co-Pt-Cr alloy magnetic film depositeddirectly onto the substrate without an intervening gallium layer. Theimage in FIG. 4 does not show any clearly defined topology.

The effect of the gallium underlayer on the magnetic film layer isbelieved to be due to the disparity of conditions for film nucleationand growth on the surface of the gallium spheres and on the siliconoxide, and by possible shadowing effects due to the spherical shape ofthe gallium surface features.

An important consideration in the manufacture of a magnetic medium isthe affect each of the layers has with regard to the coercive force ofthe magnetic material layer and the coercive squareness ratio.

FIGS. 5 to 9 are graphical representations of the magnetic properties ofa 750Å thick layer of Co-Pt-Cr alloy film deposited on an underlayer ofgallium of different average thickness deposited on a silicon dioxidesubstrate.

In FIG. 5 there is no gallium underlayer, the magnetic layer isdeposited directly onto the substrate. In FIG. 6 there is a 25Å averagethickness of the gallium layer. In FIG. 7 there is a 50Å averagethickness gallium layer. In FIG. 8 there is a 100Å average thickness ofthe gallium layer. In FIG. 9 there is a 200Å average thickness of thegallium layer.

The increase of coercivity H due to the gallium underlayer becomesapparent when comparing the value of 485 Oe for the sample without agallium underlayer in FIG. 5 with the values of 1384 Oe, 1292 Oe, 1829Oe and 1680 Oe for the samples in FIGS. 6 though 9 where the averagegallium layer thickness is 25Å, 50Å, 100Å and 200Å respectively.Referring to the graphical representations, there is also manifest adecrease in the B-H loop squareness as the gallium underlayer thicknessis increased as indicated by the lower squareness ratio (SR) andcoercive squareness ratio (S*) values with increasing average galliumlayer thickness as shown in the following Table I.

                  TABLE I                                                         ______________________________________                                        Ga Thick-  Hc                                                                 ness (AÅ)                                                                            (Oe)          SR     S*                                            ______________________________________                                         0          485          .8237  .8283                                          25        1384          .7110  .8251                                          50        1292          .7470  .6996                                         100        1829          .6752  .6676                                         200        1680          .6808  .5839                                         ______________________________________                                    

While increased thickness of the gallium underlayer positively affectstopology and coercivity of the magnetic thin films, excessive underlayerthicknesses may drastically reduce remanent magnetization, and thereforethe read-write characteristics of the magnetic medium. The effect is dueto excessive reactions between the transient liquid metal and themagnetic alloy, resulting in the overall reduction of the magneticphase. In such instances metal film interlayer 16 of chromium,palladium, tantalum, molybdenum, or vanadium, with chromium being thepreferred material, is deposited on the transient liquid metal film 12deposited on substrate 10 as shown schematically in FIG. 10. Themagnetic film layer is then deposited onto the metal film interlayer.While not limited to the elements mentioned above, such interlayer isrequired to form an intermetallic compound with the gallium which isrich in gallium, with the preferred atomic composition being Ga6B, whereB is the barrier element, such as chronium. The result is earlysolidification of the liquid underlayer even with thin barrier layer,since 1 atom of Cr combines with 6 atoms of Ga in a solid compound.

FIG. 11 is a scanning electron microscope image of the magnetic filmlayer of a medium composed of a silicon dioxide substrate on which a100Å average thickness underlayer of gallium has been deposited,followed by a barrier metal film interlayer of 100Å thick chromium layeron which a 750Å thick Co-Pt-Cr alloy magnetic film layer has beendeposited.

A comparison of FIG. 3C and FIG. 11 shows that the morphology issubstantially the same as the film deposited on a 100Å thick underlayerof gallium without a chromium interlayer. Moreover, the addition of thechromium interlayer permits control of the surface topology over a widerange of surface roughness to improve the tribology while stillmaintaining high coercivity of the film. Curve 20 shows the coercivity(Hc) as a function of gallium underlayer thickness with a 300Å thickCo-Pt-Cr alloy magnetic film layer. Curve 22 shows the coercivity (Hc)as a function of gallium underlayer thickness with a 100Å thick layer ofchromium deposited on the gallium underlayer and a 300Å thick Co-Pt-Cralloy magnetic film layer deposited or the chromium layer. Curve 22shows that high coercivity is also achieved with the chromium barrierinterlayer.

Additional measurements have shown that the chromium layer seals thegallium underlayer without adversely affecting the magnetizationcharacteristics of the medium.

The tribological performance of the magnetic films with the topologycontrolled according to the present invention is superior to theperformance achieved with conventional magnetic films.

Results of tribology tests on a smooth glass substrate are shown in thetable below.

                  TABLE II                                                        ______________________________________                                        Start/Stop Test measurements, after 3000                                      start and stop cycles.                                                        Ga (Å)                                                                            Cr (Å)  CoPtCr (Å)                                                                           Stiction (g)                                   ______________________________________                                         0      0           600        >20                                             50     200         600        4                                               50     0           600        4.2                                            100     0           600        3.8                                            200     200         600        2.05                                           ______________________________________                                    

As shown in the table above, the use of a transient liquid metalunderlayer during manufacture of a magnetic medium, with or without achromium or other metal interlayer, reduces the stiction as compared toa magnetic medium manufactured without the use of a transient liquidmetal underlayer. It will be apparent to those skilled in the art thatit is possible by masking of the substrate t limit the deposits of thetransient liquid metal underlayer to predetermined locations on thesubstrate. As a result, the surface roughness of the magnetic medium canbe varied at different locations on the medium.

While there has been described and illustrated a preferred magneticmedium and a method of manufacturing such media and variations thereof,it will be apparent to those skilled in the art that furthermodifications and variations are possible without deviating from thebroad scope of the present invention which shall be limited solely bythe scope of the claims appended hereto.

What is claimed is:
 1. A magnetic storage medium comprising:asubstantially non-wettable substrate; a transient liquid metal layer ofa thickness substantially in the range of 25-300 angstroms depositedupon said substrate while said substrate is maintained at a temperaturein excess of the melting point of said liquid metal to form adistribution of disconnected molten metal spherical structures; anintermediate metal film layer deposited upon said transient liquid metallayer; and a magnetic film layer subsequently deposited on saidintermediate metal film layer, whereby said intermediate metal filmlayer controls reaction of said transient liquid metal and said magneticfilm layer.
 2. A magnetic storage medium as set forth in claim 1 whereinsaid transient liquid metal layer is selected from the group consistingof gallium, indium, tin, bismuth, lead, cadmium, mercury, selenium,tellurium and their alloys with other metals including silver,palladium, platinum and gold, and binary and ternary compounds of theliquid metals.
 3. A magnetic storage medium as set forth in claim 1,wherein said magnetic film layer is an alloy of which cobalt is is amajor constituent
 4. A magnetic storage medium as set forth in claimwherein said magnetic film layer is selected from the group consistingof Co-Pt-Cr, Co-Cr, Co-Ni-Cr, and Co-Re.
 5. A magnetic storage medium asset forth in claim 1 wherein said transient liquid metal comprisesgallium.
 6. A magnetic storage medium as set forth in claim 1 whereinsaid transient liquid metal comprises indium.
 7. A magnetic storagemedium as set forth in claim 1 wherein said substrate is selected fromthe group consisting of silicon dioxide, glass, polymers and metalsubstrates treated in such a manner as to be rendered substantiallynon-wettable to said transient liquid metal.
 8. A magnetic storagemedium as set forth in claim 1 wherein said thickness is selected forcontrolling the topology of said magnetic film layer.
 9. A magneticstorage medium as set forth in claim 8 wherein said transient liquidmetal layer is deposited at a preselected region of said substrate. 10.A magnetic storage medium as set forth in claim 1, wherein saidintermediate metal film layer is selected from the group consisting ofchromium, palladium, tantalum, molybdenum and vanadium.
 11. A magneticstorage medium as set forth in claim 1, wherein said transient liquidmetal is deposited at a preselected region of said substrate.
 12. Amagnetic storage medium having controllable surface surface topologycomprising:a substantially non-wettable substrate; a transient liquidmetal layer of a thickness substantially in the range of 25-300angstroms deposited upon said substrate while said substrate ismaintained at a temperature in excess of the melting point of saidliquid metal to form a distribution of discontinued molten metalspherical structures, wherein said transient liquid metal is selectedfrom the group consisting of gallium, indium, thin, bismuth, lead,cadmium, mercury, selenium, tellerium and their alloys with other metalsincluding silver, palladium, platinum and gold, and binary and ternarycompounds of the liquid metals; an intermediate metal film layerdeposited upon said transient liquid metal layer, and a magnetic filmlayer subsequently deposited upon said intermediate metal film layer,wherein said intermediate metal film layer controls reaction of saidtransient liquid metal and said magnetic film layer and saidpredetermined thickness is selected for controlling the topology of saidmagnetic film layer.
 13. A magnetic storage medium as set forth in claim12 wherein said intermediate metal film layer is selected from groupconsisting of chromium, palladium, tantalum, molybdenum and vanadium.14. A magnetic storage medium as set forth in claim 13 wherein saidmagnetic layer is an alloy of which cobalt is a major constituent.
 15. Amagnetic storage medium as set forth in claim 14 wherein said magneticlayer is selected from the group consisting of Co-Pt-Cr, Co-Cr, Co-Ni-Crand Co-Re.